This invention relates to a gauge to measure and indicate the divergence of the axis of a bore in a bowling ball from a radius of the bowling ball.
Persons familiar with the bowling art are aware that the finger grip holes are drilled in bowling balls at selected distances from one another and at selected angles which best suit the grip of an individual user. In order properly to drill these holes in a bowling ball, it is necessary to know their spacing apart, and also to know their orientation relative to a true radius where they intersect the surface of the ball. In the trade it is customary to read out these dimensions and to set up drilling machinery either as a function of angles, or more usually as the number of inches by which the axis of the bore misses the center of the ball itself. This is of course a theoretical measurement because one has no access to this region, but is serves the purpose when used as a measurement convention.
It is an object of this invention to provide a gauge which can quickly and accurately measure the divergence of the axis of a bore from a radius of the bowling ball so as to provide a reading which can be set into a drilling machine for drilling a similar hole in another ball.
A gauge according to this invention includes a reference plate which has a pair of contact points for contacting the surface of the bowling ball. Between the contact points there is a pivot axis. These points and the pivot axis are substantially upon a surface having a radius approximately that of an average bowling ball. An expandable plug is pivotally mounted to the reference plate at said pivot point. This plug has an axis and pair of axially extending side walls. The side walls are substantially parallel to one another and are movable toward and away from one another while remaining substantially parallel so as to expand against and contact the inside wall of said bore. This action aligns the plug axis with the axis of the bore. A pointer is mounted to the plug and a scale is provided on the reference plate which cooperates to indicate the divergence, when the reference plate is in proper contact with the surface of the bowling ball.
According to a preferred but optional feature of the invention, the plug includes a frame and two contactors. Each contactor has a contact surface parallel to the axis of the plug, and bias means biases the contactor apart from one another so as to seek the wall of the bore.